Cleaner apps are not so much a bad idea, it's more that there's a lot of bad cleaner apps. Really bad. And the reality is that they are rarely, in fact almost never, actually needed . I have run most of my devices their whole life and never used a cleaner. A couple of times since starting with Android v1.0. They just don't make a significant difference in a good way. But a bad one can cause havoc.

That said, if for some reason you think you have to have a cleaner (you don't) SD Maid is the best - and safest - one I've seen. Unlike other so-called cleaners, SD Maid only does what it should do - clear out junk files, clean up databases, etc. It does not try to do things it shouldn't. There's no RAM cleaner/optimizer, no cache cleaner automatically deleting useful cache files. It does not run in the background, only when used. No nag ads. Just a powerful set of useful tools for doing useful things.

But...it is a powerful set of tools. And remember, use of tools like this are seldom, usually never, actually needed. Use it very rarely, with extreme care and at your own risk!

Thanks for the info. I wasn't necessarily thinking one was definitely needed it was more a curiosity as to whether one would be beneficial or not really more than anything else. It's definitely good to know one isn't essential so I will probably just leave my phone without using one.